The invention relates to an oscillator for producing rectangular pulses with a Schmitt trigger. It is known how a rectangular shaped pulse voltage can be produced from a sinusoidal input voltage for example, with the aid of a Schmitt trigger circuit. A Schmitt trigger circuit changes from its starting condition when a certain triggering level is reached and then goes back into the starting condition when a cut-off level is reached.
Often a clock pulse generator is necessary for integrated digital circuits and its frequency can be tuned in a certain range around the basic frequency f.sub.0. The variation range is .+-.30% for example. Furthermore the integrated circuit should be constructed as far as possible so that it only has a single external connection to which the time-determining external components can be connected.